Volume control for radio circuits



Filed July 2, 195o Sept. v17, 1935. E. F. CARTER Er AL VOLUME CONTROLFOR RADIO CIRCUITS WMWSQ W.

BY @M .DQ/W 4 M ATTORNEYS Patented Sept. 17, 1935 UNITED STATES PATENTOFFICE VOLUME CONTROL FOR RADIO CIRCUITS Emmett Finley Carter, Flushing,N. Y.,

and

Application July 2, 1930, Serial No. 465,352

21 Claims.

This invention pertains to radio receivers, more especially to radioreceivers adapted for radio broadcast reception.

A primary object of the invention is to provide a receiver of the typespecified embodying an improved type of continuously variable volumecontrol element whereby the volume of the received signal may be quicklyand easily adjusted over a wide range of values extending fromexceedingly low to high intensities.

In the past two general types of volume control elements have beenprovided for radio broadcast receivers. One type that has been utilizedcomprises a variable resistance such as a rheostat bridged across theinput section to the receiver. .Another and frequently used typecomprises a potentiometer arrangement for varying the potential of thecathodes or screen grids of the radio frequency amplier tubes.

The first arrangement is objectionable in that it is difficultmechanically to construct a suitable high resistance rheostat which Willpermit variation of the signal intensity over the desired range ofvalues and which at the same time embodies the desirable features ofeconomy and ruggedness. The rheostat method of volume control is furtherobjectionable in that the high resistance utilized renders the receivernoisy. Due to the capacity and resistance of the connecting wires,volume control at low intensities becomes particularly difficult. Theadjustment of volume by the rheostat method is in general without effectupon the inherent noise of the set as a consequence of which a reductionof signal intensity does not produce a corresponding reduction of noisein the set, so that the ratio of noise to signal intensity increases asthe volume is reduced.

The seco-nd arrangement, that of varying the potential of the cathodesor screen grids is objectionable in that any adjustment of the controlelement changes the operating conditions for the tubes. This causes thetubes in general to be operated at points on their characteristic curvesother than the linear portion thereof, which results in anintermodulation of signals with. consequent distortion. As a furtherobjection to volume control by this method it has been found in practicethat in order to provide a desirable range of volume adjustment it isnecessary to work the tubes almost to their cutoff points which causesthe signal to be greatly distcrted as the cutoff point is approached.

The present invention provides a volume control which overcomes theabove objections in that it is extremely economical of construction,provides continuous volume reduction over a very wide range of valuesand causes the tubes always to be operative at the straight portion ofthe tube characteristic, thereby insuring freedom from .7 distortion,modulation, and crosstalk troubles in the radio frequency stages, Thedesign of the space-current supply circuit for the tubes is simplifiedsince with the control of the present invention there is no variation inplate current i() drawn by the radio-frequency tubes. The control may bemade smooth, noiseless, free from Wear, and with any desired law ofvariation in attenuation with angular position of the control dial.

The invention is particularly applicablel to the l5 modern type of radiobroadcast receiver wherein the various portions of the radioefrequencyamplier are completely shielded from each other by positioning the samein individual metal compartments. The invention is furthermore es 20pecially applicable to the receivers wherein capacitive coupling isutilized to couple the outputJ circuit of one tube with the inputcircuit of the succeeding tube, the output circuit of each tube being ina'shielding compartment distinct from 25 that housing the input circuitof the succeeding tube.

As applied to a receiver of this type, the invention comprises avariable coupling condenser connecting the output section of the firstradio-fre- 3o quency stage to the input section of the next succeedingstage. This condenser is of unique construction and consists of a sleeveof insulating material such as bakelite fitted into an aperture in theshield separating the output section of the rst radio-frequency tubefrom the input section of the immediately succeeding tube. A metalplunger is slidable within the bore of the insulating sleeve in suchmanner that an insulated conductive end portion thereof within the boremay be adjusted from one shielding com partment to the other. Aconductive collar is positioned about the insulating sleeve in theshielding compartment containing the output circuit of the firstradio-frequency amplifier tube 45 and is conductively connected to theanode electrode thereof. The conductive end portion of the plunger isconnected by a flexible lead to the grid electrode of the succeedingradio-frequency tube. 50

As a result of this arrangement it will be obvious that the couplingcapacity may be varied by movement of the plunger. When the plunger isin such position that the insulated end portion and the `conductivecollar are situated in different shielding compartments, the capacitivecoupling between the first and second tubes is reduced almost to aerodue to the interposition of the shield therebetween. When, however, theplunger is withdrawn until the insulated end portion is situated beneaththe metal collar the coupling capacity between tubes is a maximum; andfor any intermediate setting of the plunger arm, of course, the couplingcapacity lies between the two values. It has been found in practice thatby adjusting the capacity in this way the received volume may be variedover a range of values having a ratio of as much as 20,000 to 1.

Having thus described the invention in general terms, reference will nowbe had to the drawing for a detailed explanation of a specificembodiment thereof wherein:

Figure l shows partly in circuit diagrammatic form a radio broadcastreceiver embodying the novel volume ccntrol of the present inventioninterposed between the rst and second radiofrequency stages;

Figure 2 shows a longitudinal cross-section of the control element;

Figures 3 and 4 show a side elevation and an end elevation respectivelyof a modiied form of the volume control element;

Figure 5 is a fragmentary view of Figure 1 disclosing a modified form ofthe invention wherein the volume control is interposed between theantenna circuit and the input to the first radiofrequency stage.

Referring to Figure 1, there is shown a radio receiver comprising aradio-frequency amplifier and detector unit A, an audio-frequencyamplifier B, and a loud speaker unit L,

The radio-frequency amplier unit A com prises two stages ofradio-frequency amplication consisting of screen grid tubes V1 and V2 incascade connection working into a screen grid detector tube V3. Eachtube comprises an anode I, cathode 2, grid 3, screen grid 4, and lamentor heater element 5. The laments 5 are connected in multiple over leadsE to a suitable source of power P for heating the tubes. Likewise, theanodes I of the tubes V1 and V2 are connected over a lead l to the powersource P for supplying space-current to the tubes; the screen grids 4are connected over a lead 8, and the cathodes 2 over a lead 9 to thepower source for applying suitable potentials thereto. Theaudio-frequency amplier B is connected by means of conductors I0 to thepower source for supplying the necessary potentials to theaudio-frequency amplifier tubes and also the eld current over leads IIto the loud speaker unit L which is of the dynamic type.

An antenna I2 and ground I3 are connected to opposite terminals of theprimary winding of a radio-frequency transformer T1, the secondary ofwhich is connected between grid 3 and cathode 2 of tube V1. A variablecondenser Ci is connected across the secondary winding L1 of transformerT1 for tuning the same. The plate electrode I of tube Vi is connectedthrcugh a radiofrequency choke coil E1 and thence to lead 1. In additionthe plate electrode I of tube V1 is also connected through the specialvolume control condenser D1 of the present invention to the gridelectrode 3 of the succeeding tube V2. Connected between the grid 3 andcathode 2 of tube V2 is a tunable resonant circuit comprising inductanceL2 and variable capacity C2 in parallel electrical connection.

The plate electrode of tube V2 is connected through a radio-frequencychoke coil E2 similar to El to lead l, and is further connected througha ixed coupling capacity D2 to the grid electrode of the succeeding tubeV3. A tunable circuit comprising inductance La and capacity C3 is 5associated with the input section of tube V3, one side of the tunablecircuit being connected directly to the grid electrode 3 of tube V3 andthe other side being connected through a resistance Ifl shunted by acapacity n to the cathode, the 1U latter elements being adapted to causethe tube V3 to function as a detector tube. The output section or tubeV3 comprising the plate I and the cathode 2 are connected over leads I5to the input section of the audio-frequency amplifier B, 15 the outputof which, in turn, is connected by means of leads I6 to thevoice-frequency winding of the loud speaker L.

The radio-frequency unit A is completely housed within a grounded metalshielding structure S divided by suitable walls or interposed screensinto shielding compartments S1 to Se inclusive. The resonant circuits LCare individually housed within compartments Si, S3 and S5 respectively,While each tube V together with d its output coil E is housed within acompartment S2, S4 O1' Se.

The capacities n are high-frequency .by-passi; condcnscrs which serve toprevent undesired coupling effects between the various ele-ments ci g,the amplifier which tend to produce undesirable f' ned oscillations. Thecapacity n connected across the output section or" tube V3 serves topass. radio-ireduency currents and thereby prevent the same from beingimpressed upon the 35 cucliofrenuency amplifier The condensers C1 C3,inclusive, arc mechanically connected by a uni-control device U forsimultaneously tuning all of the circuits LC alike.

The inductance of each chcke coil E is selected 4U t with theplate-to-ground capacity of the coiv ondir tube V itis resonant at afrequency L "ble range for the resmore since each coil shielded from thenext succeeding tuned cir 45 cuit LC, the only coupling between circuitsis through the corresponding coupling capacity D. The elements E, LC andD are suitably proportioned te produce uniform anzplication over thefrequency range of the tunable circuit LC, the mi, e'fuoui'i" ciamplification being determined by and nai to the magnitude ci capacityD. By capacity D from a value about 7 i, ads to low a value as po.`ible, the amplication may be controlled over a wid.. ,I range ci valueswithout aiecting the trennen characteristics of the receive 2 A suitablere of volume control may be obtained in this mann;Y by varying only oneof the coupling' condensers D such, for example, as the condenser D1. m

Referring specically to Figures 1 and 2, the condenser D1 comprises aninsulating sleeve .TI mounted within an aperture in shielding wall i'ielectrically screening the output circuit ci tube V1 from the inputcircuit ci tube V2. A plunger is slidably positioned within the sleeve te plunger consisting of a main conductive portion M insulated by amember i8 from a conductive ond portion N.

A compression spring IS positioned about projecting portion of member Mby reac against the end oi sleeve F forces the head ci member M at alltimes .into engagement with a cam 2| mounted upon a shaft 22 projectingthrough the screen S and provided upon its outer end with a knob 23 foradjusting the position of the plunger.

The sleeve F is provided with turned depressions housing the metalcollars H, I and J positioned thereabout. Collars I-I and I are locatedin the same shielding compartment Sz with the output circuit of tube V1,while collar J is positioned in the shielding compartment S3 housing thetuned circuit L2 C2 connected to the input circuit of tube V2. 'Ihe endportion N is connected by a flexible lead 2d to the grid electrode oftube V2 while collar I positioned adjacent screen l? but insulatedtherefrom is connected to the plate electrode of tube V1. Collars H andJ are grounded as is also the conductive portion M of the plunger K asshown in Figure l.

As a result of this arrangement it will be observed that adjustment ofthe knob 23 varies the capacity electrostatically coupling the elementsI and N thereby adjusting the capacitive coupling existing between theoutput circuit of tube V1 and input circuit of tubev V2.

With the plunger in the position shown in Figure l the capacity betweenelements I and N is a minimum due to the interpcsition of the groundedshield Il' therebetween, which effective-ly shields one said elementfrom the other. This shielding eiect is made more complete by the factthat the end of conductive member M substantialh7 fills up the hole inscreen il which houses the sleeve F.

If now the knob 23 is so rotated that member N displaced from shieldingcompartment S3 to shielding compartment S2, the capacity betweenelements I and N will gradually increase to a maximum value attainedwhen member N is situated substantially beneath member I thus providinga maximum degree of coupling between the stages V1 and V2 of theamplifier A. Figure 2 shows the plunger adjusted to a positionintermediete between the maximum and minimum capacity values.

Due to the extremely low capacity obtainable between elements I and Nwhen the screen Il is interposed therebetween, it is possible to obtainan extremely wide range of adjustment for the signal intensity impressedfrom the output circuit of tube V1 through the coupling capacity D1 uponthe input circuit of tube V2. The minimum capacity adjustment of thecondenser is further reduced by the provision of the grounded collars Iland J and the grounded portion M of the plungor. 'Ihis results from thefact that with the plunger in the position shown in Figure l there is arelatively large capacity to ground from the grid ele-ctrode of tube V2due to the fact that the end portion N is situated directly beneath thegrounded collar J. Likewise there is a relatively large capacity toground from the plate electrode of tube V1 due to the fact that theconductive portion M of the plunger is situated beneath collars I andI-I. These grounded capacities serve to reduce the voltage impressedacross the coupling capacity D1 between stages comprising the elements Iand N.

Figures 3 and 4 disclose a modied form of the invention wherein theplunger K comprises a single conductive member slidably housed within asleeve F consisting of the insulating plates 25 and E@ held together inrigid assembly by means of screws 2l. The sleeve F is positioned withinan aperture in the shield H. A conductive plate R is mounted upon theouter side of the sleeve F on one side of the shield Il.

In the operation of this device the plunger K is conductively connectedto the plate electrode of tube V1 and the plate R to the grid electrodeof tube V2, or the connections may be reversed if desired. With thisarrangement it will be obvious that the capacity between elements K andR is adjusted from a maximum value with a portion of the plunger Kprojecting through the screen and positioned adjacent the plate R, to alow minimum value with the plunger wholly withdrawn to the opposite sideof the screen.

By suitably shaping the cam 2l the volume may be caused to vary in anydesired manner with angular adjustment of the knob 23.

With the arrangement of Figure l, the full signal intensity is impressedupon the input to the first radio frequency tube V1. This may beundesirable where powerful stations operate in the vicinity of thereceiver or where powerful signals are being received. Under suchconditions the circuit modification of Figure 5 becomes prei"- erable,in which the Volume control condenser D1 variably couples the antennacircuit to the input of tube V1.

In Figure 5 the antenna circuit is similar to that of Figure l. The highpotential terminal of the tuned circuit L1 C1, instead of beingconnected directly to the grid of tube V1 as formerly, is now coupled tothe collar I of condenser D1 mounted in the partition separatingscreening compartments S1 and S2, the conductive end portion ci thepiston K being connected by flexible lead 2t to the grid of tube V1. Aradio-frequency choke coil E3 is connected between grid and cathode oftube V1 to suitably adjust the input impedance relations.

We claim:

l. A multi-stage thermionic amplifier wherein the output section of onestage is variably coupled capacitively to the input section of thesucceeding stage, means electrically shielding said sections including aconductive screen interposed therebetween, said capacity comprising axed element connected to one said section and positioned on the sameside of said screen therewith, and a conductive plunger connected to theother said section and insulatedly slidable through a slot in saidscreen adjacent said xed element, for varying the capacity from amaximum value with said plunger adjacent said xed element, to a lowminimum value with the plunger withdrawn to the opposite side of saidscreen.

2. A multi-stage thermionic amplifier comprising vacuum tubes in cascadeconnection, each having anode, cathode and grid electrodes, meanselectrically shielding the output section of one said tube from theinput section of the succeeding f tube, said means including aconductive screen interposed therebetween, a variable capacity connectedfrom the anode electrode of said rst tube to the grid electrode of saidsucceeding tube, said capacity comprising a fixed element connected toone said electrode and positioned on the same side of said screentherewith, and a conductive plunger connected to the other saidelectrode and insulatedly slidable through a slot in said screenadjacent said fixed element for varying the capacity from a maximumvalue with said plunger positioned adjacent said fixed element, to a lowminimum value with the plunger withdrawn to the opposite side of saidscreen.

3. A multi-stage thermionic amplifier comprising vacuum tubes in cascadeconnection, each having a grid and a cathode comprising said inputsection and said cathode and an anode comprising an output section, animpedance connected to the output section of one said tube, an impedanceconnected to the input section of the succeeding tube, meanselectrically shielding said output and said input sections including aconductive screen interposed therebetween, a variable capacity connectedfrom the anode electrode of said first tube to the grid electrode ofsaid second tube, said capacity comprising a xed element connected toone said electrode and positioned on the same side of said screentherewith, and a con-- ductive plunger connected to the other saidelectrode insulatedly slidable through a slot in said screen adjacentsaid fixed element for varying the capacity from a maximum value withsaid plunger positioned adjacent said iixed element to a low minimumvalue with plunger withdrawn to the opposite side of said screen.

4. A multi-stage thermionic ainpliiier comprising vacuum tubes incascade connection each having grid and cathode electrodes comprising aninput section and said cathode and an anode electrode comprising anoutput section, an impedance connected to the output section of one saidtube, a resonant circuit tunable over a range in frequency connected tothe input section of succeeding tube, means electrically shielding saidoutput section from said tunable circuit, said means including aconductive screen interposed therebetween, a variable condenserconnected from the anode electrode of said first to the grid electrodeof said succeeding tube, said condenser` comprising a fixed elementconnected to one said electrode and positioned on the same side of saidscreen therewith, and a conductive plunger con-- nected to the othersaid electrode and insulatedly slidable through a slot in said screenadjacent said iixed element for varying the capacity from a maximumvalue with a portion of said plunger positioned adjacent said fixedelement, to a low minimum value with the plunger wholly withdrawn to theopposite side of said screen.

5. In combination, a pair of electrical circuits, means electricallyshielding said circuits including a conductive screen interposedtherebetween grounded to one side of each said circuit, a variablecondenser capacitively coupling the ungrounded sides of said circuitscomprising, a fixed element connected to one said circuit and positionedon the same side of the screen therewith, and a conductive plungerconnected to the other said circuit and insulatedly slidable through aslot in said screen for varying the capacity between said fixed elementand said plunger from a maximum value with a portion of said plungerpositioned adjacent said fixed element to a low minimum value with saidplunger displaced to the opposite side of said screen.

6. In combination, a pair of electrical circuits, means electricallyshielding said circuits including a conductive screen interposedtherebetween grounded to one side of each said circuit, a variablecondenser capacitively coupling the ungrounded sides of said circuitscomprising, an insulating sleeve mounted in an aperture in said screen,a plunger slidable within said sleeve including an insulated conductiveend portion, adapted to be displaced from one side of said screen to theother, a conductive collar placed about said sleeve on one side of saidscreen and connected to the said circuit adjacent thereto, meansconnecting said conductive end portion to the other said circuit wherebythe capacity of said condenser may be varied from a maximum to a lowminimum value as said conductive end portion is displaced from one sideto the other of said screen.

7. A multi-stage high-frequency amplifier tunable over a range infrequency comprising vacuum tubes in cascade connection wherein theoutput circuit of a rst tube includes an impedance tuned to a frequencyslightly below said range and the input circuit of the succeeding tubeincludes a resonant circuit tunable over said frequency range, meanselectrically shielding said output and input circuits, said meansincluding a conductive screen interposed therebetween, a capacityconnecting the anode electrode of said first to the grid electrode ofsaid succeeding tube, said capacity comprising a stator positioned onthe same side of said screen with the said electrode connected thereto,and a conductive plunger connected to the other said electrode andinsulatedly slidable through a slot in said screen adjacent said statorfor varying said capacity from a maximum value with said plungerpositioned adjacent said stator to a low minimum value with said plungerwholly withdrawn to the opposite side of said screen whereby the signalintensity impressed from said output upon said input circuit may bevaried over a wide range.

8. An ampliiier in accordance with claim 7 wherein said impedance,capacity and tuned circuit are proportioned to provide substantiallyuniform amplification over said range in frequency.

9. A multi-stage high-frequency amplifier com- "f prising therrnionictubes in cascade connection each having a grid and cathode comprising aninput section, and said cathode and an anode comprising an outputsection, 2, nxed impedance connected in the output circuit of one tubeand a tunable impedance in the input circuit of the succeeding tube,means electrically shielding said output and input circuits including aconductive screen interposed therebetween grounded to said cathodes,means adjustably controlling the signal intensity impressed upon saidinput from said output circuit comprising, a variable condenserconnected from the anode of said first to the grid of said succeedingtube, said condenser consisting of a xed element positioned fi on thesame side with and connected to one said electrode, and a conductiveplunger connected to the other said electrode and insulatedly slidablethrough a slot in said screen, for adjusting the capacity or saidcondenser from a maximum to a low minimum value as said plunger isdisplaced from a position adjacent said xed element to the opposite sideof said screen therefrom.

10. A multi-stage high-frequency amplifier comprising thermionic tubesin cascade connection each having a grid and cathode included in aninput circuit and said cathode and an anode included in an outputcircuit, a fixed impedance connected in the output circuit of one tubeand a tunable impedance in the input circuit of the succeeding tube,means electrically shielding said output and input circuits including aconductive screen interposed therebetween grounded to said cathodes,means adjustably controlling the signal intensity impressed upon saidinput from said output circuit comprising, a variable condenserconnected from the anode of said iirst to the grid of said succeedingtube, an insulating sleeve positioned within an aperture in said screen,a conductive collar placed thereabout on the same side of said screenwith and connected to one said electrode, a plunger slidable within saidsleeve comprising a conductive end portion insulated from a conductivemain portion, said end lll portion being connected to the other saidelectrode for adjusting the coupling capacity between said electrodesfrom a maximum to a low minimum value as said end portion is displacedfrom a position adjacent said collar to the opposite side of said screentherefrom.

11. In an amplifier as set forth in claim 12 additional means forfurther reducing the minimum capacity adjustment of said condenserconsisting of a second conductive collar positioned about said sleeve onthe same side with and longitudinally displaced from said first collar,and a third conductive collar positioned about said sleeve on theopposite si-de of said screen, said main plunger portion beingpositioned on the same side of said screen with said first and secondcollars, means grounding said second and third collars and said mainplunger portion to said screen whereby with said end portion and saidfirst collar positioned on opposite sides of said screen there existsrelatively large capacities from said anode and grid electrodes toground at said shield through said second and third collars and theconductive portions of said plunger which capacities greatly reduce theeffect of said coupling capacity between said electrodes.

12. The combination in a radio receiving system of an exciting circuitincluding an impedance, an absorbing circuit including a secondimpedance, a shield therebetween, and means comprising a variablecapacity coupling said irnpedances for varying the signal intensityimpressed from said exciting upon said absorbing circuit and for varyingthe volume of reproduction over a wide range.

13. The combination in a radio receiving system of a high frequencyexciting circuit and an absorbing circuit, at least one of which istunable over a range in frequency, a pair of impedances individual tosaid circuits, a shield member therebetween, and means comprising avariable capacity connected between said impedances for adjusting thesignal intensity impressed from said exciting upon said absorbingcircuit and for varying the volume of reproduction over a wide range.

14. The combination in a radio receiving system of a high-frequencyexciting and a high-frequency absorbing circuit, at least one of whichis tunable over a range in frequency, Aa pair of magnetically uncoupledimpedances individual to said circuits, a shield therebetween, aconductive path extending from a point of the first to a point of thesecond impedance, and means comprising a variable capacity connectedfrom a different point of the first to a different point of the secondimpedance for adjusting the signal intensity irnpressed from saidexciting upon said absorbing circuit and for varying the volume ofreproduction over a Wide range.

15. The combination in a radio. receiving system of a high-frequencyexciting and a highfrequency absorbing circuit, at least one of which istunable over a range in frequency, a pair of magnetically uncoupledimpedances individual to said circuits with a conductive screeninterposed therebetween grounded to a point of each said impedance, anda variable capacity connected from a different point of said first to adifferent point of said second impedance for adjusting the signalintensity impressed from said exciting upon said absorbing circuit, saidcapacity comprising a fixed plate connected to one said impedanceelement and positioned on the same side of the screen therewith, and avariable plate conl nected to the other said impedance and slidablyadjustable through an aperture in said screen from one side to the otherthereof.

16. The combination in a radio receiving system of a Vacuum tubeamplifier stage, an input 2 circuit connected thereto, a preceding radiocircuit feeding thereinto, a shield member therebetween, a couplingcondenser cooperating therebetween and comprising separate xed memberson opposite sides of said shield and a movable 2 plate member connectedto said input circuit and movable between said fixed plates through saidshield.

17. The combination in a radio receiving system of a plurality of radiocircuits and a variable f" coupling member operating for connectiontherebetween, comprising a plurality of separate electrically insulatedstationary plates, a movable plate cooperating therebetween and arotatable handle member for adjusting the position of 2' and having aplate adapted to project more or if' less beyond one side of saidshield.

21. The combination in a radio receiving system of a vacuum tube havingan output circuit, a coil therein, a second vacuum tube having an inputcircuit, a coil in said input circuit, a shield between said coils, aflexible conductor connected at one end to said input circuit and havingthe other end thereof movable, and means for moving the movable end ofsaid flexible conductor to se- 5.

lectively connect said input circuit around said shield to said outputcircuit.

